An image forming system includes a fixing device. The fixing device thermally fixes toner onto a sheet. The fixing device includes a fixing member and a pressing member. The pressing member presses a sheet.
The temperature of the fixing member is controlled on the basis of a temperature distribution in a longitudinal direction of the fixing member. The temperature of the fixing member is more preferably detected at a plurality of locations in the longitudinal direction.
For example, the fixing device may include a plurality of temperature measurement sensors fixed to predetermined positions. However, in this case, there is a problem in that the temperature of a location where the temperature measurement sensors are not disposed cannot be measured. If the number of temperature measurement sensors is increased, there is a problem in that component cost is increased.
For example, the fixing device may move a single temperature measurement sensor in the longitudinal direction. In this case, it is necessary to perform position control of the temperature measurement sensor. However, there is a problem in that a motor which can control sensor position is expensive.
For example, there may be a configuration in which a position measurement sensor is combined with a cheap motor. However, the position measurement sensor is required to measure any position in a movement range of the temperature measurement sensor. There is a problem in that the position measurement sensor requires a large installation space. There is also a problem in that the position measurement sensor is expensive.